1. Field of the Invention
The present invention pertains to electronic devices, such as power electronic devices (e.g., multi-level power inverters), that employ series connected gate oxide-isolated active power semiconductor devices, and, in particular, to a method and circuit for driving series connected gate oxide-isolated active power semiconductor devices in such electronic devices while maintaining voltage sharing across each series connected gate oxide-isolated active power semiconductor device, voltage isolation and, in some embodiments, controller redundancy.
2. Description of the Related Art
A number of different power conversion modules/systems are well known for converting power from one form to another. For example, a multilevel power inverter is a power electronic device that is structured to produce AC waveforms from a DC input voltage. As another example, an active front end (also called a controllable rectifier or PWM rectifier) is a power electronic device wherein AC waveforms are converted to DC voltages. Such power conversion modules/systems are used in a wide variety of applications, such as, without limitation, variable speed motor drives.
Many power conversion modules/systems employ power electronics that require (i) voltage isolation between the controlling logic signals and the output power channel, and/or (ii) series connection of independently controlled/driven active power semiconductor devices to achieve voltage ratings. Such isolation and independent control are often provided by what is known as a gate drive circuit. More specifically, a gate drive circuit is a circuit that is used in a power electronic device to convert logic level control signals into the appropriate voltages for switching the active power semiconductor devices of the power electronic device, and, in most cases, to provide voltage isolation so that the logic signals are not connected to the potentially dangerous high voltage on the power circuit.
A number of gate drive circuits/techniques for providing the above described isolation and/or control functionality have been developed. For example, one such technique includes applying fiber optic transceivers or other opto-isolators with dedicated isolated power supplies to achieve the isolation. Another technique uses a transformer to transfer a voltage directly across the barrier while maintaining galvanic isolation. Still another technique employs a combination of the above, where transformers are used for the digital on-off signal, while power is transferred separately with an isolated power source. These known techniques, however, are costly and often do not provide the precise synchronization needed for control of series connected of active power semiconductor devices.